1. Field of the Invention
This invention relates to electrical tools, and more particularly concerns a combination tool for safely extracting fuses of the cartridge type and testing the extracted fuse.
2. Description of the Prior Art
Cartridge-type fuses are comprised of a circular cylindrical body extending between two metal end caps, and an internal conductor centered within said body and extending between said end caps. The cylindrical body is electrically insulated from said end caps and internal conductor. In use, the fuse is emplaced in a manner such that the end caps are secured by terminals, which are usually spring-loaded.
Tools for gripping the cylindrical body of the fuse, and pulling it away from securement by the terminals have earlier been disclosed. For example U. S. Pat. Nos. 4,314,385 and 4,414,698, concern a device for pulling automobile fuses which generally handle 12 volts of electrical current. Such low voltages involve relatively little hazard. Also, relatively little force is required to extract the fuse from the securing terminals. Accordingly, the construction of such devices is not dictated by the requirements of sturdiness and safety. It is also to be noted that the puller tools of the aforesaid Patents are limited to use with fuses of just one particular cylindrical diameter.
Large cartridge-type fuses, as used in industrial applications, may handle high amperage currents at up to about 600 volts. The handling of such fuses involves considerable risk. A plier-type tool for extracting large fuses is disclosed in U.S. Pat. No. 2,023,916 to Dante. The Dante tool also has provision for testing the fuses, namely testing the continuity of electrical conductivity between the end caps. However, the mode of testing requires that the line voltage be directed through the tool. Such mode of testing is hazardous.
The Dante tool further permits the operator to test the fuse while it is still emplaced within a high voltage electrical circuit. Such testing involves considerable risk to the operator. It also requires considerable knowledge on the part of the operator as to where the test pins should be placed. For example, as shown in FIG. 6 of Dante, the test pins 28 and 29 cannot merely be placed in contact with the metal end caps of an emplaced single fuse, the reason being that this will always show continuity, regardless of the condition of the fuse. Therefore, Dante's tool can only be employed by a skilled electrician.
U. S. Pat. No. 2,588,559 to Needham discloses a battery-operated device for testing the continuity of fuses. In the illustrated embodiment, cartridge fuses of only two different sizes can be tested. This represents a severe limitation of the Needham device because it is often necessary to be able to test cartridge fuses of numerous different sizes. Furthermore, the only reason the Needham device can test two different length fuses is that it is predicted upon use with those styles of cartridge fuses that have a cylindrical body of smaller diameter than the diameter of its end caps. However many styles of fuses have a cylindrical body and end caps of substantially equal diameter, and accordingly could not be tested in multiple sizes by the Needham device.
Devices such as disclosed in U. S. Pat. No. 2,901,294 designed specifically for the testing of fuses, generally have means for contacting the end caps, and an electrical circuit that includes a visual indicator. The manipulation of the testing tool relative to the fuse may be time-consuming, depending upon the exact design of the tool. Furthermore, in those testing devices having lead wires or equivalent extension contact means, there is the possibility that the contact means may inadvertently bridge dangerously high current carriers.
It is accordingly an object of the present invention to provide a tool for safely pulling and testing cartridge-type fuses of various sizes that handle large electrical currents.
It is another object of this invention to provide a tool as in the foregoing object wherein the testing of a pulled fuse can be quickly achieved.
It is still another object of the present invention to provide a tool of the aforesaid nature whose construction requires that the fuse be pulled before testing, thereby thwarting improper and hazardous use of the tool.
It is a further object of this invention to provide a tool of the aforesaid nature which is of sturdy, simple construction amenable to low cost manufacture, and easy to manipulate.
These objects and other objects and advantages of the invention will be apparent from the following description.